Machine to Machine (M2M) communication is a future development trend in intelligent communication. The Machine Type Communication (MTC) function needs to be supported in the Universal Mobile Telecommunication System (UMTS) and its Long Term Evolution (LTE) system. An MTC device (MTC terminal) can have a part of a number of M2M communication characteristics, e.g., low mobility, a small amount of transmission data, insensitivity to a communication delay, requirement for extremely low power consumption, etc.
1. MTC
MTC, which is a new communication idea, is intended to integrate a variety of communication technologies, e.g., machine to machine communication, machine controlled communication, human to machine interaction communication, mobile intercommunication, etc., to thereby drive the development of social production and life styles. Future human to human communication services are expected to account for only ⅓ of the entire market of terminals, whereas inter-machine (small-bandwidth system) communication services may account for a higher proportion of communication.
An existing mobile communication network is designed, for example, the capacity of the network is determined, for interpersonal communication. If the mobile communication network is expected to support small-bandwidth system communication, then the mechanism of the mobile communication system will be optimized for the characteristics of small-bandwidth system communication to thereby better enable small-bandwidth system communication with an insignificant or no influence upon legacy interpersonal communication.
Some possible characteristics of MTC communication are currently identified as follows:
The MTC terminal has low mobility;
The MTC terminal transmits data with the network side in a controllable period of time, that is, the MTC terminal can only access to the network in a network specified period of time.
The MTC terminal transmits data with the network side without high requirement on real time data transmission, which means temporal tolerance.
The MTC terminal is limited in energy, so power consumption thereof is required to be extremely low.
Only small data is transmitted between the MTC terminal and the network side.
The MTC terminal can be managed per group.
A real MTC terminal can have one or more of the characteristics above.
2. Paging Mechanism
There are two states of a terminal in the LTE system, i.e., the RRC_connected (RRC stands for Radio Resource Control) state and the RRC_idle state.
The terminal operating in the RRC_idle state primary detects paging of the network side. The terminal typically detects paging in the Discrete Receive (DRX) mode for the purpose of saving power, where only one sub-frame (1 ms) of each paging cycle is in a reception state, and the remaining periodicity is in non reception state, as illustrated in FIG. 1.
As illustrated in FIG. 2, for a paging procedure, paging is initiated by a core network entity, and the paging message is firstly transmitted to an eNB (evolved NodeB). Where the paging message carries DRX configuration specific to a User Equipment (UE, i.e., terminal). In the LTE system, the eNB compares the DRX cycle with a DRX cycle configured in a system message, and transmits the paging message at the shorter one of the DRX cycles.
The calculation of the position where the terminal receives paging is associated directly with a System Frame Number (SFN), and an International Mobile Subscriber Identity (IMSI) of the terminal (see the 3GPP Protocol TS 36.304). The paging identifier of the terminal (UE_ID) is derived in the equation of UE_ID=IMSI mod 1024. The IMSI is a globally unique identifier of the terminal including no more than 15 digits, each of which is an integer between 0 and 9, for example, IMSI=12345678901234.
The terminal can only receive a paging message at most once in a paging cycle. However for the terminal operating in some scenario, for example, the terminal operating underground, in a shopping mall, or at the corner of a building, a radio signal may be seriously shielded and thus significantly attenuated so that the terminal can not communicate with the network, but deep coverage by the network in such a scenario may result in a considerable increase in deployment cost of the network, including an added expense of equipments, an added cost of network planning, an added expense of manual maintenance, etc; and the M2M services will be deployed in the LTE network along with the evolvement of wireless communications, so it will be desirable to effectively extend coverage by the network in later LTE-based wireless communications to thereby address the problem of covering the terminal operating in the scenario above.
For these MTC terminals requiring for coverage enhancement, the paging message received only once can not be decoded correctly, so that the terminals may miss paging and thus can not be called, thus degrading a user experience, and the overall performance of the system.
The UE has a chance to receive paging at the beginning of a paging cycle, and the base station can retransmit for the terminal several times in at least one other paging cycle after the paging cycle, so that the terminal will have a further chance to receive paging if the terminal has failed to receive the first paging. However for those MTC terminal required for coverage enhancement, if the retransmission is performed in this way, then it can not be guaranteed that the paging can be received correctly with the number of retransmissions, and there may be a significant delay in the current retransmitting paging, such as a delay of tens of seconds.